#!/usr/bin/env bash

#################################################################################
# This script is run by git before a commit is made.                            #
# Does some housekeeping tasks before a commit is made.                         #
#                                                                               #
#                                   FEATURES                                    #
# Updates the "updated" field in the front matter of .md files.                 #
# Compresses PNG files with either oxipng or optipng if available.              #
# Runs subset_font if config.toml has been modified.                            #
# Updates the README if the line numbers for the language section have changed. #
#################################################################################

# Function to exit the script with an error message.
function error_exit() {
    echo "ERROR: $1" >&2
    exit "${2:-1}"
}

# Function to extract the date from the front matter.
function extract_date() {
    local file="$1"
    local field="$2"
    grep -m 1 "^$field =" "$file" | sed -e "s/$field = //" -e 's/ *$//'
}

##################################################################
# Compress PNG files with either oxipng or optipng if available. #
# Update the "updated" field in the front matter of .md files.   #
#          https://osc.garden/blog/zola-date-git-hook/           #
##################################################################

# Check if oxipng is installed.
png_compressor=""
if command -v oxipng &> /dev/null; then
    png_compressor="oxipng -o max"
elif command -v optipng &> /dev/null; then
    png_compressor="optipng -o 7"
fi

# Get the modified .md and .png files, ignoring "_index.md" files.
modified_files=$(git diff --cached --name-only --diff-filter=M | grep -E '\.(md|png)$' | grep -v '_index.md$')

# Loop through each modified .md or .png file.
for file in $modified_files; do
    # If the file is a PNG and png_compressor is set, compress it and add it to the commit.
    if [[ "$file" == *.png ]] && [[ -n "$png_compressor" ]]; then
        $png_compressor "$file" || error_exit "Failed to compress PNG file $file"
        git add --force "$file" || error_exit "Failed to add compressed PNG file $file"
        continue
    fi

    # If the file is an .md file, update the "updated" field in the front matter.
    if [[ "$file" == *.md ]]; then
        # Get the last modified date from the filesystem.
        last_modified_date=$(date -r "$file" +'%Y-%m-%d')

        # Extract the "date" field from the front matter.
        date_value=$(extract_date "$file" "date")

        # Skip the file if the last modified date is the same as the "date" field.
        if [[ "$last_modified_date" == "$date_value" ]]; then
            continue
        fi

        # Update the "updated" field with the last modified date.
        # If the "updated" field doesn't exist, create it below the "date" field.
        if ! awk -v date_line="$last_modified_date" 'BEGIN{FS=OFS=" = "; first = 1} {
            if (/^date =/ && first) {
                print; getline;
                if (!/^updated =/) print "updated" OFS date_line;
                first=0;
            }
            if (/^updated =/ && !first) gsub(/[^ ]*$/, date_line, $2);
            print;
        }' "$file" > "${file}.tmp"
        then
            error_exit "Failed to process $file with AWK"
        fi

        mv "${file}.tmp" "$file" || error_exit "Failed to overwrite $file with updated content"


        # Stage the changes.
        git add "$file"
    fi
done

#########################################################
# Run subset_font if config.toml has been modified.     #
# https://welpo.github.io/tabi/blog/custom-font-subset/ #
#########################################################
if git diff --cached --name-only | grep -q "config.toml"; then
    echo "config.toml modified. Running subset_font…"

    # Call the subset_font script.
    ~/bin/subset_font -c config.toml -f static/fonts/Inter4.woff2 -o static/

    # Add the generated subset.css file to the commit.
    git add static/custom_subset.css
fi

################################################################################
# Update the README if the line numbers for the language section have changed. #
################################################################################

# File paths and names.
config_file="config.toml"
config_readme="README.md"

# Ensure the required files are present.
[ ! -f "$config_file" ] && error_exit "$config_file not found!"
[ ! -f "$config_readme" ] && error_exit "$config_readme not found!"

# Determine the line numbers for relevant sections in config.toml.
lang_start_line=$(grep -n "^\[languages.es\]$" "$config_file" | cut -d: -f1)
extra_start_line=$(grep -n "^\[extra\]$" "$config_file" | cut -d: -f1)
lang_end_line=$((extra_start_line - 2))

# Extract currently documented line numbers from README.
documented_lines=$(grep -o 'https://github.com/welpo/tabi/blob/main/config.toml#L[0-9]*-L[0-9]*' "$config_readme" | grep -o 'L[0-9]*-L[0-9]*')
doc_start_line=$(echo "$documented_lines" | cut -d'-' -f1 | tr -d 'L')
doc_end_line=$(echo "$documented_lines" | cut -d'-' -f2 | tr -d 'L')

# Ensure that the variables are set and are numbers.
if [[ ! $lang_start_line =~ ^[0-9]+$ ]] || [[ ! $doc_start_line =~ ^[0-9]+$ ]] || [[ ! $lang_end_line =~ ^[0-9]+$ ]] || [[ ! $doc_end_line =~ ^[0-9]+$ ]]; then
    error_exit "Line number variables are not set correctly."
fi

# Update the README if there's a discrepancy in the line numbers.
if [ "$lang_start_line" -ne "$doc_start_line" ] || [ "$lang_end_line" -ne "$doc_end_line" ]; then
    if ! perl -pi -e "s|https://github.com/welpo/tabi/blob/main/config.toml#L[0-9]*-L[0-9]*|https://github.com/welpo/tabi/blob/main/config.toml#L$lang_start_line-L$lang_end_line|g" "$config_readme"; then
        error_exit "Perl processing failed for $config_readme"
    fi
    
    # Add updated README to commit.
    git add "$config_readme"
fi